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Discussion Starter #1 (Edited)
Am researching a conversion plan for a 40' pusher school bus. I like the idea of sticking with Cummins because of the reputation, availability of parts and "reasonable prices" (for the older engines). I would like to stay away from the new engines because of the exorbitant prices for parts - especially electronics. I have been poking around a lot of forums and have come up with this combination. Does this seem like it will do the trick? I plan on doing a lot of interstate traveling so would like the bus to cruise at least 65 mph without sounding like it would blow up. 80 would be awesome - speed limit in Montana, Nevada, N Dakota, Idaho is 75 or 80 in places, but I can live with 65. Does this seem reasonable? I am hoping that the 8.3 has enough extra power to enable it to be durable as well as efficient, also that by being Cummins, I will be able to find support at almost every truck stop in North America.
 

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10 years ago, I drove school bus. We were taught that the law stated the maximum speed was 65 MPH. I do not know it that was an AZ law or a federal law. Maybe look for a school bus from a rural district that transported kids on the interstate, that way the bus would be geared for sustained higher speeds (just a thought, I drove them locally, and the newer diesel buses would easily hit 65 on the road out of town).

And some words on used school buses. Our small school district (rural Arizona) would replace the troublesome buses and keep the older buses for the local grade school runs. My little preschool bus qualified for AZ antique plates (over 25 years old).

In some states, there are state laws on how old and/or how many miles a school bus can have and remain in service (hauling kids).
 

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We have a few pushers with 8.3's, auto, they have higher axle ratios(no clue on ratio, possibly could get) than 5.9 Cummins, will easily go 75 or 80.

Ed
 

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I would think the 8.3 was not all that common in buses. The 5.9 is plenty strong enough to give you the power for road speeds. The ideal engine to be on the lookout for would be the CPL1553. That was the 230 HP 5.9 which did come in buses or medium duty trucks. That is the most powerful road use 5.9 12 valve Cummins offered. With a little tinkering you could probably have 300 HP. Seems like the auto transmission typically found mated to that engine was the Allison 3060 which is very strong. Some of the lighter duty Allisons may not like the 650 lb ft of torque that engine puts out.
 

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My (very) limited experience showed that the rear engine (pusher) buses got a bigger engine than the front engine (puller) buses. The pusher buses were built heavier and were the go-to choice for out of town trips.
 

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Russ, that's probably true. Seem like most of the CPL1553 powered buses were pushers. The one big thing most of these buses lack is aerodynamics. Sort of like pushing a cement block down the road.
 

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Discussion Starter #7 (Edited)
So what is likely to be the difference in mpg between a 5.9 a 6.7 and an 8.3, both with turbos and after coolers,same transmission, same rear end, etc? Let's throw the 466DT in there too. Consider a bus with a GVWR of 27,000 pounds, and towing a 5,000 pound box trailer?
Another thing I like about the idea of the 8.3...a true exhaust brake can be installed.
 

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So what is likely to be the difference in mpg between a 5.9 a 6.7 and an 8.3, both with turbos and after coolers,same transmission, same rear end, etc? Let's throw the 466DT in there too. Consider a bus with a GVWR of 27,000 pounds, and towing a 5,000 pound box trailer?
Another thing I like about the idea of the 8.3...a true exhaust brake can be installed.
I have no real world experience, we just filled the tank, I don't think anyone kept track of MPG in our district (and I mostly drove the short bus - always thought that was an appropriate end of my working says). In general, the smaller the engine, the harder it has to work. The bigger engine will be appreciated out on the interstate, especially on the steep grades (you might even get to pass a SWIFT semi-truck). Hopefully, someone has data on pusher bus MPG.
 

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The 6.7 is a modern computer controlled engine. You probably don't want to go there. The 5.9 6bt can be built to just about any power level imaginable. It's peak torque typically come on in the 1700 RPM range and normally works out to be 2.5 times HP. The 6ct 8.3 has peak torque coming full on at 1300 RPM and it is 2.85 times HP. In other words, the 8.3 will have more pulling power at lower RPM. Factory rev limits on all these is factory set at around 2500 RPM. You'd need to compute what your engine speed will be at your desired road speed. Have to figure in tire size, differential ratio, and transmission gearing. The closer you can run the engine near it's peak torque, the better the fuel mileage. The 6bt like to run in the 1700-2000 RPM range. I'd guess the 6ct would happier in the 1300-1600 RPM range.
 
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